<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>JQuery 回到顶部效果</title>
  <link rel="stylesheet" href="css/stylesheets/back_top.css" />
  <script src="framework/js/jquery-3.1.1.min.js"></script>
  <script src="js/back_top.js"></script>
</head>
<body>
<div class="box">
<img src="img/tb_bg.png" />
</div>
<a href="javascript:;" id="btn" title="回到顶部"></a>
</body>
</html>